Pierre Godard

We report the development and synchrotron integration of a longitudinal magneto-optical Kerr effect (MOKE) magnetometer designed for in situ operation during x-ray diffraction (XRD) experiments under multiaxial mechanical loading. The optical layout, magnetic-field geometry, and mechanical compatibility were optimized to enable synchronized acquisition of MOKE hysteresis loops, XRD lattice strain, and digital image correlation (DIC) data within the constrained environment of a diffraction goniometer. The capabilities of the platform are demonstrated on a Co/W thin film deposited on a flexible Kapton® substrate subjected to equi-biaxial tensile loading. The combined MOKE–XRD–DIC measurements reveal three distinct mechanical regimes from elastic strain transfer to partial relaxation and ultimately full mechanical fragmentation, each associated with a characteristic magnetic response. Post-mortem image analysis provides a quantitative description of fragment morphology, linking crack topology to the evolution of magnetic properties and highlighting the role of fragment size, shape anisotropy, and mechanical isolation in strain-dependent magnetic behavior. The present approach establishes a multi-scale framework that integrates surface magnetometry, structural probes, and real-space imaging, opening new opportunities for studying magneto-mechanical coupling and damage-driven functional evolution in flexible magnetic thin films.

Flexible magnetoelectronics face a major challenge in maintaining functionality under mechanical strain. This research investigates how biaxial multicracking affects the magnetic properties of nanometric thin films, specifically by separating magnetoelastic from magnetostatic effects. Using a unique experimental platform, we show that in magnetostrictive Co films, the magnetic behavior is dominated by stress‐induced magnetoelastic effects. In contrast, in non‐magnetostrictive films, the magnetic changes only appear once multicracking begins, allowing us to demonstrate the magnetostatic contributions from fragmentation. Our findings reveal that the variation in the saturation field correlates directly with fragment shape. This work demonstrates that fragmentation is not just a failure mechanism but a controllable process whose magnetic effects can be understood and leveraged for designing next‐generation flexible devices.

Micropillar compression is a method of choice to understand mechanics at small scale. It is mainly studied with electron microscopy or white-beam micro-Laue X-ray diffraction. The aim of the present article is to show the possibilities of the use of diffraction with a coherent X-ray beam. InSb micropillars in epitaxy with their pedestals (i.e. their support) are studied in situ during compression. Firstly, an experiment using a collimated beam matching the pillar size allows determination of when the sample enters the plastic regime, independently of small defects induced by experimental artefacts. A second experiment deals with scanning X-ray diffraction maps with a nano-focused beam; despite the coherence of the beam, the contributions from the pedestal and from the micropillar in the diffraction patterns can be separated, making possible a spatially resolved study of the plastic strain fields. A quantitative measurement of the elastic strain field is nevertheless hampered by the fact that the pillar diffracts at the same angles as the pedestal. Finally, no image reconstructions were possible in these experiments, either in situ due to a blurring of the fringes during loading or post-mortem because the defect density after yielding was too high. However, it is shown how to determine the elastic bending of the pillar in the elastic regime. Bending angles of around 0.3° are found, and a method to estimate the sample's radius of curvature is suggested.

Lens-less imaging of crystals with coherent X-ray diffraction offers some unique possibilities for strain-field characterization. It relies on numerically retrieving the phase of the scattering amplitude from a crystal illuminated with coherent X-rays. In practice, the algorithms encode this amplitude as a discrete Fourier transform of an effective or Bragg electron density. This short article suggests a detailed route from the classical expression of the (continuous) scattering amplitude to this discrete function. The case of a heterogeneous incident field is specifically detailed. Six assumptions are listed and quantitatively discussed when no such analysis was found in the literature. Details are provided for two of them: the fact that the structure factor varies in the vicinity of the probed reciprocal lattice vector, and the polarization factor, which is heterogeneous along the measured diffraction patterns. With progress in X-ray sources, data acquisition and analysis, it is believed that some approximations will prove inappropriate in the near future.

Strain and defects in crystalline materials are responsible for the distinct mechanical, electric, and magnetic properties of a desired material, making their study an essential task in material characterization, fabrication, and design. Existing techniques for the visualization of strain fields, such as transmission electron microscopy and diffraction, are destructive and limited to thin slices of the materials. On the other hand, nondestructive x-ray imaging methods either have a reduced resolution or are not robust enough for a broad range of applications. Here we present x-ray ptychographic topography, a method for strain imaging, and demonstrate its use on an InSb micropillar after microcompression, where the strained region is visualized with a spatial resolution of 30 nm. Thereby, x-ray ptychographic topography proves itself as a robust nondestructive approach for the imaging of strain fields within bulk crystalline specimens with a spatial resolution of a few tens of nanometers.

Metallic thin films deposited onto polymeric substrates find important technological applications as stretchable microelectronic devices. Academic research on these systems has mainly focused on uniaxial tensile tests, though biaxial stress states are generally applied during service. We study in this article the strain ratio effect on nanocrystalline 50 nm-thick gold thin films supported on a polyimide: equibiaxial applied strain vs uniaxial applied strain. The mechanical behaviors are compared with digital image correlation, x-ray diffraction, and relaxation tests, giving the true and lattice strains, insights into strain heterogeneities, and leading plasticity mechanisms. Moreover, two load–unload cycles were performed to deconvolute the different parts contributing to the signals. It is shown that though the samples were transversely isotropic (i.e., isotropic in the plane of the applied strains), the work-hardening properties are very different, the micro-plastic regime being greatly reduced in the equibiaxial test. This is illustrated with the elastic limits and with the fact that an equibiaxial test presents at equivalent von Mises strain higher stress relaxation and a decrease in strain heterogeneities.

The phenomena associated with strain-mediated multiferroic behavior have been quantitatively studied by combining synchrotron x-ray diffraction (XRD), ferromagnetic resonance (FMR) and macroscopic strain measurements (digital image correlation) in a magnetoelectric composite (Ni film on PZT substrate). The ferroelectric and piezoelectric strains have been studied by analyzing the evolution of x-ray patterns (peak intensities and shifts), while the magnetic response is studied by FMR (energy shift of the resonance), during in situ application of electrical voltage. Being given the intrinsic selective phase nature of XRD, the lattice strains have also been measured in the Ni film and have been found to be comparable to the macroscopic one (full transmission from the PZT substrate). The PZT strain has been successfully separated into two contributions, i.e. ferroelectric and lattice strains, the first one being five times higher than the second one. Moreover the last is itself composed of two sub-contributions: pure piezoelectric effect and ferroelectric strain in surrounding grains (strain transfer at grain boundaries). Finally, through in situ FMR measurements, we showed that the ferroelectric contribution to the strain-mediated magnetoelectric response is ten times higher than the pure piezoelectric one.